Here is this thread:
http://www.hometheaterforum.com/htforum/showthread.php?s=&postid=2961058#post2961058
Eva, so acceleration is not frequency related but didn't you say that it's nuch higher for lower frequencies ?
Doesn't that make it frequency related ?
--Sincerely,
http://www.hometheaterforum.com/htforum/showthread.php?s=&postid=2961058#post2961058
Eva, so acceleration is not frequency related but didn't you say that it's nuch higher for lower frequencies ?
Doesn't that make it frequency related ?
--Sincerely,
**We are in the subwoofer forum here, 1khz doesn’t matter a bit**
most subwoofers are measured a 1khz don’t know why?
most subwoofers are measured a 1khz don’t know why?
Vaughan:
You probably misunderstood me, I said that acceleration is only SPL dependent and is required to be constant for a flat SPL response. Mark Seaton explains it quite well in the thread of the link, alotugh he makes a mistake because all the magnitudes involving in radiating a sine-wave are sine waves (including acceleration and speed). It's speed what increases linearly as frequency is decreased (as opposed to popular claims) and cone displacement suffers a quadratic increase.
Hayden:
This is a common mistake. First, those PA 18" drivers that I mentioned are intended to be useable as all-in-one mid-bass plus subwoofer, something like a wide-range bass driver covering 30 to 400Hz. This has sonic advantages against a normal sub because the crossover is avoided and the bass is always coherent with the sub-bass (providing excellent bass-drum playback). To make things funnier, most of these drivers may be horn loaded... 😀
Second, our hearing sensitivity increases progressively from 100Hz to 1Khz with a slope between 6dB/oct and 12dB/oct, and this means that if you feed normal music to a subwoofer with a 1st or 2nd order 100Hz lowpass filter, 1Khz components from the music are going to be perfectly audible through the sub despite the filter. That's because our hearing sensitivity cancels out filter action, thus any good subwoofer must be as free of colouration as possible in the mid-bass range, particularly in the 100Hz to 500Hz range, otherwise very steep filters are required (with the difficulties associated).
You probably misunderstood me, I said that acceleration is only SPL dependent and is required to be constant for a flat SPL response. Mark Seaton explains it quite well in the thread of the link, alotugh he makes a mistake because all the magnitudes involving in radiating a sine-wave are sine waves (including acceleration and speed). It's speed what increases linearly as frequency is decreased (as opposed to popular claims) and cone displacement suffers a quadratic increase.
Hayden:
This is a common mistake. First, those PA 18" drivers that I mentioned are intended to be useable as all-in-one mid-bass plus subwoofer, something like a wide-range bass driver covering 30 to 400Hz. This has sonic advantages against a normal sub because the crossover is avoided and the bass is always coherent with the sub-bass (providing excellent bass-drum playback). To make things funnier, most of these drivers may be horn loaded... 😀
Second, our hearing sensitivity increases progressively from 100Hz to 1Khz with a slope between 6dB/oct and 12dB/oct, and this means that if you feed normal music to a subwoofer with a 1st or 2nd order 100Hz lowpass filter, 1Khz components from the music are going to be perfectly audible through the sub despite the filter. That's because our hearing sensitivity cancels out filter action, thus any good subwoofer must be as free of colouration as possible in the mid-bass range, particularly in the 100Hz to 500Hz range, otherwise very steep filters are required (with the difficulties associated).
Those are typically PA type "subwoofers," not true subwoofers meant to produce sound down below 20hz.
Eva you are right that displacement, cone velocity, and acceleration are all "sin" functions. I say "sin" because if cone displacemnt is given by sin, its derivative is usually stated as cosine and not some phase shifted sin function.
It's likely done to claim higher sensitivity.
Isn't that just infra? Anything between 20 - 40 Hz would be true sub afaik.
Wkr Johan
Eva,
You probably misunderstood me, I said that acceleration is only SPL dependent and is required to be constant for a flat SPL response. Mark Seaton explains it quite well in the thread of the link, alotugh he makes a mistake because all the magnitudes involving in radiating a sine-wave are sine waves (including acceleration and speed).
So acceleration, the ability for the driver to track the input signal is just a function of SPL ? Is there any theory behind this ?
Perhaps you could help me to understand this a little better. Because I am getting all hung up on motor BL here. In this very thread, car analogies have been made to show that increasing BL could overcome mass of bigger drivers.
Now I find that mass isn't the concern at all. That mass doesn't play a part in determining how quick a driver responds. Is that correct ? Can you let me know why mass doesn't play a role in determining driver acceleration ?
If you could try and explain it as simply as you can I would appreciate it. I must admit though that there is a lot of misinformation out there.
--Sincerely,
You probably misunderstood me, I said that acceleration is only SPL dependent and is required to be constant for a flat SPL response. Mark Seaton explains it quite well in the thread of the link, alotugh he makes a mistake because all the magnitudes involving in radiating a sine-wave are sine waves (including acceleration and speed).
So acceleration, the ability for the driver to track the input signal is just a function of SPL ? Is there any theory behind this ?
Perhaps you could help me to understand this a little better. Because I am getting all hung up on motor BL here. In this very thread, car analogies have been made to show that increasing BL could overcome mass of bigger drivers.
Now I find that mass isn't the concern at all. That mass doesn't play a part in determining how quick a driver responds. Is that correct ? Can you let me know why mass doesn't play a role in determining driver acceleration ?
If you could try and explain it as simply as you can I would appreciate it. I must admit though that there is a lot of misinformation out there.
--Sincerely,
Aceleration is not "the ability for the driver to track the input signal", aceleration is a physical magnitude whose mathematical definition is dv/dt (where v is speed, t is time and d stands for derivative).
Also, it's not easy to reply to your questions. You have to understand that the motor applies an instantaneous force (proportional to the instantaneous voice coil current) not only to the moving mass of the own cone and the voice coil, but also to the spring formed by the spider and cone surround, to the spring formed by the air inside the box (assuming a sealed one) and to the additional spring formed by the outer air. This is quite a complex "load".
Note that, since the required acceleration for flat frequency response is constant with frequency, and the required speed is inversely proportional to frequency, moving mass by itself can't produce any high frequency roll-off. As I have previously mentioned, what causes big drivers to show poor HF performance is non-uniform cone displacement and the HF energy being absorbed or stored in cone materials instead of radiated to the air as it propagates from the inner to the outer regions of the cone.
Smaller drivers suffer exactly from the same pitfalls, but HF performance is improved because mechanical energy has to travel shorter distances.
Also, it's not easy to reply to your questions. You have to understand that the motor applies an instantaneous force (proportional to the instantaneous voice coil current) not only to the moving mass of the own cone and the voice coil, but also to the spring formed by the spider and cone surround, to the spring formed by the air inside the box (assuming a sealed one) and to the additional spring formed by the outer air. This is quite a complex "load".
Note that, since the required acceleration for flat frequency response is constant with frequency, and the required speed is inversely proportional to frequency, moving mass by itself can't produce any high frequency roll-off. As I have previously mentioned, what causes big drivers to show poor HF performance is non-uniform cone displacement and the HF energy being absorbed or stored in cone materials instead of radiated to the air as it propagates from the inner to the outer regions of the cone.
Smaller drivers suffer exactly from the same pitfalls, but HF performance is improved because mechanical energy has to travel shorter distances.
Maybe I'm missing something here but doesn't the postion of a cone moving at, for this example one frequency (w), Amplitude(Y), have the following equation of motion y(displacement)=Y*sin(wt)
If so then Acceleration would be a = -Y*w^2sin(wt), doesn't this mean it is frequency dependent?
nunayafb said:
It does not work that way.
Assuming a piston diaphragm with uniform movement and a voice coil with negligible inductance and constant BL, driven by a sine wave, then we have a constant moving mas "M" over wich a force defined by an ondulatory function f=I*BL*sin(wt) is acting ("I" is voice coil current amplitude and "BL" is motor force factor in Newtons/Ampere).
As acceleration is just force/mass :
a = (I*BL/M) * sin (wt)
Where (I*BL/M) is a constant that does not depend on frequency, thus acceleration is not frequency dependent, it only depends on the amplitude of the input signal.
Finally, by integrating the previous expression across "t" we can calculate instantaneous speed, and integrating again across "t" we obtain instantaneous cone position:
v = -(1/w) * (I*BL/M) * cos (wt)
x = -(1/w^2) * (I*BL/M) * sin (wt)
Thus the amplitude of v is inversely proportional to w and the amplitude of x is inversely proportional to w^2
p.s. It may seem a bit funny, but these equations also demonstrate that the cone actually "moves" in the opposite direction of the force being applied by the motor, since x is 180 degrees out of phase respect to a (this is only valid for AC signals).
Aceleration is not "the ability for the driver to track the input signal", aceleration is a physical magnitude whose mathematical definition is dv/dt (where v is speed, t is time and d stands for derivative).
Then what determines the ability for the driver to track the input signal ?
I just need these things to be put into perspective for me. Because I am still hung up in understanding the flaws surrounding the myth.
Dan Wiggins says that acceleration is proportional to SPL. So SPL determines who quick a driver can accelerate. Correct ?
But if a 10" driver can't move as much air as an 18" to reproduce a 40 hz sinewave or an explosion at that frequency, then which driver would be faster ?
The 18" driver because it moves more air and thus can accelerate faster ?
--Sincerely,
Then what determines the ability for the driver to track the input signal ?
I just need these things to be put into perspective for me. Because I am still hung up in understanding the flaws surrounding the myth.
Dan Wiggins says that acceleration is proportional to SPL. So SPL determines who quick a driver can accelerate. Correct ?
But if a 10" driver can't move as much air as an 18" to reproduce a 40 hz sinewave or an explosion at that frequency, then which driver would be faster ?
The 18" driver because it moves more air and thus can accelerate faster ?
--Sincerely,
The 10" driver needs to move faster to produce as much SPL as the 18" driver does. However, if they are both limited to the same excursion level, then they will accelerate the cone equally as fast, AFAIK (in which case the 18" driver produces higher SPL).Vaughan said:
If the 18" driver has identical excursion levels compared to the 10", the surely they will accelerate at the same speed within their respective passband ?
So because the 18" driver more often than not has more exursion levels, it doesn't need to accelerate quickly to reproduce low frequencies. And because the 10" driver has less excursion and thus needs to move much quicker to achieve the reproduce the same low frequencies, the 18" will be quicker ?
Is that right ? Are there any additional articles or threads that deal with this topic besides the "speed articles by Dan Wiggins" and the soundstage article ?
Are there any books that would help me to understand this myth ? Thanks again.
--Sincerely,
So because the 18" driver more often than not has more exursion levels, it doesn't need to accelerate quickly to reproduce low frequencies. And because the 10" driver has less excursion and thus needs to move much quicker to achieve the reproduce the same low frequencies, the 18" will be quicker ?
Is that right ? Are there any additional articles or threads that deal with this topic besides the "speed articles by Dan Wiggins" and the soundstage article ?
Are there any books that would help me to understand this myth ? Thanks again.
--Sincerely,
Dude you got that totally backwards.... An 18" driver needs LESS excursion to reach the same SPL as a 10" driver at the same low frequency. Therefore it will accelerate less to produce that tone because its not moving as much.
The 10" moves MUCH more because it has a smaller radiation surface. In subwoofers there's no replacement for displacement, swept air is what we're after because the pressure has to come from somewhere. Since we're not changing the amount of air, heating it, or cooling it, we must be changing volume to create pressure changes.
Because a 10" driver travels a further distance(at the same frequency mind you) to produce the same SPL as a 18" it will inherently be "faster"
In ideal conditions and keeping the frequency constant, the amount of cone displacement required for a given SPL is just inversely proportional to radiation surface. The typical radiating surface for 10" drivers is approx 300cm^2, while for 18" drivers it's typically 1200cm^2, thus there is a 4:1 cone displacement advantage.
On the other hand, moving mass figures for typical midbass/bass 10" PA drivers are between 30 and 50 grams, and moving mass figures for midbass/bass 18" PA drivers (not the ones intended only for sub duties) are typically beteen 100grams and 160 grams. This gives a 3:1 mass disadvantage to the 18" drivers.
Also, the force required to get a certain cone displacement is proportional to the moving mass and to the magnitude of the own displacement. Thus, with the same applied force, such 18" PA drivers will produce the same or slightly higher SPL than similarly built 10" PA drivers, because the surface advantage overcomes completely the mass disadvantage.
However, motor force factors are not the same. Typical 18" PA drivers show BL values in the range from 20 to 30 Newtons/Ampere, while similar 10" drivers show BL values from 10 to 20 N/A. This fact indeed produces a remarkable efficiency improvement, as the same voice coil current will produce almost 6dB higher output in the 18" drives due to increased BL.
Finally, note that Hi-Fi 10" drivers hardly feature BL values above 10N/A and are not likely to have a moving mass below 40 grams, so their efficiencies are almost always poor. Moving mass for some exotic small 8" and 10" drivers may be even above 100 grams, and people here is discussing things like adding 400 grams to their tiny 8" driver to lower the Fs at the expense of efficiency, and get a result that would be better achieved with equalization. Those are the "slow" drivers: Weak motors driving tiny cones that weight a ton.
On the other hand, moving mass figures for typical midbass/bass 10" PA drivers are between 30 and 50 grams, and moving mass figures for midbass/bass 18" PA drivers (not the ones intended only for sub duties) are typically beteen 100grams and 160 grams. This gives a 3:1 mass disadvantage to the 18" drivers.
Also, the force required to get a certain cone displacement is proportional to the moving mass and to the magnitude of the own displacement. Thus, with the same applied force, such 18" PA drivers will produce the same or slightly higher SPL than similarly built 10" PA drivers, because the surface advantage overcomes completely the mass disadvantage.
However, motor force factors are not the same. Typical 18" PA drivers show BL values in the range from 20 to 30 Newtons/Ampere, while similar 10" drivers show BL values from 10 to 20 N/A. This fact indeed produces a remarkable efficiency improvement, as the same voice coil current will produce almost 6dB higher output in the 18" drives due to increased BL.
Finally, note that Hi-Fi 10" drivers hardly feature BL values above 10N/A and are not likely to have a moving mass below 40 grams, so their efficiencies are almost always poor. Moving mass for some exotic small 8" and 10" drivers may be even above 100 grams, and people here is discussing things like adding 400 grams to their tiny 8" driver to lower the Fs at the expense of efficiency, and get a result that would be better achieved with equalization. Those are the "slow" drivers: Weak motors driving tiny cones that weight a ton.
My million dollar question is this...
Is it better (read: more efficient in terms of space and power usage) to use four 15" woofers or two 18" woofers, given similar T/S parameters including power handing and xmax for both drivers?
Is it better (read: more efficient in terms of space and power usage) to use four 15" woofers or two 18" woofers, given similar T/S parameters including power handing and xmax for both drivers?
I vote for the 15"s. While it won't likely go quite as deep, there's an advantage people sometimes miss to using a lot of drivers for bass- it disperses the excitation of the room modes to some extent. Anything that reduces or breaks up room interaction is AOK in my book. 2 18"s or 4 15"s.... either should be plenty 🙂
Eva,
this may be stupids questions but I have to make it clear.
Is VAS related to speed?
Let say I have the choice between two 15" driver, one optimised for small enclosure with a vas about 260Liters and one "old school" that have a vas of about 580liters
I just can`t give a clue about VAS of a driver and it`s sound (except the relation: high VAS=big enclosure)
And the Qms. If I understand right, high QMS woofer will have a soft suspention and low QMS will have a stiff suspention.
Lets compare a high qms vs a low qms. (supposing rest being equal)
So, If we feed one impulsion to both drivers;
the first one (highQms) will let the cone move freely and will not break the cone. That should provide good dynamic. While the other (low Qms) will have to fight against the stifness of the suspension. the first one should move faster with less distortion.
But when the impulsion is done, the high qms will take long time to stop while the low Q will stop a lot faster. should this driver sound more "precise"?
Is there a "sweet" qms that provide the best compromise?
thanks
this may be stupids questions but I have to make it clear.
Is VAS related to speed?
Let say I have the choice between two 15" driver, one optimised for small enclosure with a vas about 260Liters and one "old school" that have a vas of about 580liters
I just can`t give a clue about VAS of a driver and it`s sound (except the relation: high VAS=big enclosure)
And the Qms. If I understand right, high QMS woofer will have a soft suspention and low QMS will have a stiff suspention.
Lets compare a high qms vs a low qms. (supposing rest being equal)
So, If we feed one impulsion to both drivers;
the first one (highQms) will let the cone move freely and will not break the cone. That should provide good dynamic. While the other (low Qms) will have to fight against the stifness of the suspension. the first one should move faster with less distortion.
But when the impulsion is done, the high qms will take long time to stop while the low Q will stop a lot faster. should this driver sound more "precise"?
Is there a "sweet" qms that provide the best compromise?
thanks
When someone says suspension stiffness I think about the spring like restoring force which is defined by the Vas(equivilant acoustic compliance, in other words the equivilant volume of air which would create the same spring constant). The Qms is merely mechanical dampening, or how much the suspension and cone absorb the mechanical moving energy of the speaker and turn it into friction. I'm not exactly sure but I dont believe there is a certian "critically dampened" Qms value.
Qms is NOT how stiff the suspension is, but how well it absorbs the vibration. Think about a tuning fork, it is a very stiff peice of metal, but it resonates because there is little dampening. A peice of rubber on the other hand may have little stiffness but high dampening.
I would think something with a high Vas and high Qms would be best
Qms is NOT how stiff the suspension is, but how well it absorbs the vibration. Think about a tuning fork, it is a very stiff peice of metal, but it resonates because there is little dampening. A peice of rubber on the other hand may have little stiffness but high dampening.
I would think something with a high Vas and high Qms would be best
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